Methods of feed purification for olefin polymerization

ABSTRACT

A polymerization process is provided. For example, a polymerization process is described, including contacting olefin monomers with a supported metallocene catalyst to polymerize the olefin monomers and form a product mixture that includes polyolefins macromers or polymers, unreacted or partially reacted olefin monomers, alcohols and organohalides. The polymerization process further includes removing a portion of the product mixture to form a recycle stream and passing the recycle stream through a removal device comprising zeolite particles having pore size of from 6 to 16 Å to transfer at least a portion of the alcohols and organohalides from the recycle stream to the removal device providing a purified recycle stream having alcohols and organohalides in an amount of 1 ppm or less. The polymerization process may further include contacting at least a portion of the purified recycle stream with the supported metallocene catalyst to form polyolefins.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of Provisional ApplicationNo. 60/417,381 filed Oct. 9, 2002, the disclosure of which areincorporated by reference.

FIELD OF INVENTION

[0002] Embodiments of the present invention generally relate to feedpurification for olefin polymerization.

BACKGROUND

[0003] Methods for forming polyolefins can include passing a streamhaving olefin monomers to a polymerization reactor to contact a catalystand form the polyolefin. However, problems may arise that reduce thecatalyst efficiency. For example, high efficiency catalysts mayexperience a reduced efficiency when exposed to poisons that may bepresent in polymerization reactors. Therefore, it is desirable to removea significant portion of the poisons from an input stream prior to theinput stream entering the reactor.

SUMMARY OF THE INVENTION

[0004] In certain embodiments, a polymerization process is describedthat includes contacting olefin monomers with a supported metallocenecatalyst to polymerize the olefin monomers and form a product mixturethat includes polyolefin macromers or polymers, unreacted or partiallyreacted olefin monomers, alcohols and organohalides. That particularpolymerization process further includes removing a portion of theproduct mixture to form a recycle stream and passing the recycle streamalone or in combination with fresh monomers through a removal devicecomprising zeolite particles having a particle size of from 6 Å to 16 Åto transfer at least a portion of the alcohols and organohalides fromthe recycle stream to the removal device providing a purified recyclestream (alone or in combination with fresh monomers) having alcohols andorganohalides in an amount of 1 ppm or less. The polymerization processmay further include contacting at least a portion of the purifiedrecycle stream with the supported metallocene catalyst to formpolyolefins.

[0005] Other embodiments include a polymerization process includingcontacting a first stream with one or more removal devices to form asecond monomer stream, wherein the at least one removal device includesmolecular sieve particles having an average pore size of from 6 Å to 16Å, contacting the second monomer stream with a metallocene catalystsystem to produce polypropylene in a third stream and separatingun-polymerized propylene from the third stream to form a fourth monomerstream. The polymerization process may further include combining thefourth monomer stream with the first monomer stream to form a mixedmonomer stream and contacting the mixed monomer stream with the one ormore removal devices to form the second monomer stream.

[0006] In certain embodiments, the second monomer stream includes lessthan 1 ppm of alcohols, halogen moeties, and organohalides. In yet otherembodiments, the second monomer stream comprises less than 0.5 ppm ofalcohols, halogen moeties, and organohalides. In certain embodiments,the fourth monomer stream comprises 5 ppm or more alcohols, halogenmoeties, and organohalides.

[0007] In certain embodiments, the first monomer stream includes freshpropylene. In yet other embodiments, the first monomer stream includesalpha-olefin monomers selected from the group including ethylene,propylene, and alpha-olefin monomers having from four to sixteen carbonatoms.

[0008] In certain embodiments, the metallocene catalyst has anefficiency of greater than 500 gPP/(gcat*hr). In yet other embodiments,the metallocene catalyst has an efficiency of greater than 2500gPP/(gcat*hr). As used herein, “gPP/(gcat*hr)” is grams of polypropyleneproduced divided by the grams of catalyst consumed per hour.

[0009] In certain embodiments, the metallocene catalyst includes 1.5 wt% or less active metallocene and 12 wt % or less metal alkyl scavenger.

[0010] In certain embodiments, the first, second and third streams havea flow rate of from 3700 kg/hr to 56000 kg/hr. The fourth stream has aflow rate of from 2600 kg/hr to 55000 kg/hr.

[0011] In certain embodiments, the one or more removal devices include a13× molecular sieve. In certain embodiments, the one or more molecularsieve particles have a particle size of 8 by 14 mesh. In yet otherembodiments, the one or more removal devices include a shell having afirst support member. The first support member may be in contact with atleast a first portion of the one or more molecular sieve particles. Inaddition, the first support member may be disposed a distance from atleast a second portion of the one or more molecular sieve particles.

[0012] Yet other embodiments include a polymerization process includingcontacting a first monomer stream including propylene monomers with asupported metallocene catalyst to form a mixture includingpolypropylene, unpolymerized propylene monomers, organohalides andalcohols, providing a second monomer stream including at least a portionof the mixture and passing at least a portion of the second monomerstream through a removal device comprising molecular sieve particleshaving a pore size of from 6 Å to 16 Å to form a third stream, whereinat least a portion of the alcohols and organohalides from the secondstream are absent from the third stream. The process may further includecontacting at least a portion of the third stream with a supportedmetallocene catalyst to form additional polypropylene.

[0013] Other embodiments provide a polymerization process includingpassing a propylene feed stream through one or more removal devices toform a purified monomer stream, wherein the propylene feed streamincludes alcohols and organohalides in an amount greater than 5 ppm andthe purified monomer stream includes alcohols and organohalides in anamount less than 1 ppm and contacting the purified monomer stream with asupported metallocene catalyst to polymerize the purified monomer streamand form a product mixture that includes polypropylene macromers orpolymers, unreacted or partially reacted propylene monomers, alcoholsand organohalides.

[0014] In certain embodiments, passing the propylene feed stream throughone or more removal devices to form a purified monomer stream includescombining a first monomer stream and a second monomer stream, the firstmonomer stream including propylene monomers and the second monomerstream including unreacted or partially reacted propylene monomers,alcohols and organohalides. In yet other embodiments, passing thepropylene feed stream through one or more removal devices to form apurified monomer stream includes combining a first monomer stream and asecond monomer stream, the first monomer stream including propylenemonomers and the second monomer stream including unreacted or partiallyreacted propylene monomers, and alcohols and organohalides in an amountgreater than 10 ppm.

[0015] In certain embodiments, the process includes removing thepolypropylene macromers from the product mixture to form a recyclestream and combining the recycle stream with the propylene feed stream.

[0016] Other advantages and uses of the present invention will becomeapparent from the following detailed description and appended claims anddrawings.

BRIEF DESCRIPTION OF DRAWINGS

[0017]FIG. 1 illustrates a system that may be employed for providing acatalyst slurry to a polymerization reactor.

[0018]FIG. 2 illustrates an enlarged view of a specific example of amolecular sieve unit.

[0019]FIG. 3 illustrates a polymerization process wherein the recyclestream is mixed with a fresh feed stream to form an input stream priorto purification.

[0020]FIG. 4 illustrates an example of a system operably connected to apolymerization vessel to deliver catalyst to the polymerization vessel.

DETAILED DESCRIPTION

[0021] Various specific embodiments, versions and examples of theinvention will now be described, including preferred embodiments anddefinitions that are adopted herein for purposes of understanding theclaimed invention. It is understood, however, that for determininginfringement, the scope of the “invention” will refer to any one or moreof the appended claims, including their equivalents, and elements orlimitations that are equivalent to those that are recited. References tospecific “embodiments” are intended to correspond to claims coveringthose embodiments, but not necessarily to claims that cover more thanthose embodiments.

[0022] Embodiments of the invention include a polymerization process.The polymerization process includes passing a feed stream having olefinmonomers through a polymerization reactor to polymerize the olefinmonomers and form a polyolefin. The feed stream preferably includesolefin monomers, either alone or in combination, e.g., mixtures, havingfrom 2 carbon atoms up to 16 carbon atoms per molecule. For example, thefeed stream may include ethylene, propylene, butene, pentene, hexane,septene and/or octene. More preferably, the feed stream includespropylene monomers. In certain embodiments, the feed stream includespropylene monomers in an amount of from 85 wt % to 90 wt %. In otherembodiments, the feed stream includes propylene monomers in an amount of95 wt % or more.

[0023] The polymerization process may be carried out in any type ofpolymerization system including, but not limited to, a solution, gasphase or slurry process, or combinations thereof. Typically, in a gasphase polymerization process, a continuous cycle is employed wherein onepart of the cycle of a reactor system, a cycling gas stream, otherwiseknown as a recycle stream or fluidizing medium, is heated in the reactorby the heat of polymerization. This heat is removed from the recyclecomposition in another part of the cycle by a cooling system external tothe reactor. The gaseous stream containing one or more monomers may becontinuously cycled through a fluidized bed in the presence of acatalyst under reactive conditions. The gaseous stream is withdrawn fromthe fluidized bed and recycled back into the reactor. Simultaneously,polymer product is withdrawn from the reactor and fresh monomer is addedto replace the polymerized monomer. Alternatively, other types of gasphase polymerization processes can also be used.

[0024] Slurry polymerization typically involves forming a suspension ofsolid, particulate polymer in a liquid polymerization medium, to whichmonomers and optionally hydrogen, along with catalyst, are added. Thesuspension (which may include diluent) can be intermittently orcontinuously removed from the reactor where the volatile components canbe separated from the polymer and recycled, optionally after adistillation, to the reactor.

[0025] In a specific embodiment, a slurry process may be carried outcontinuously in one or more loop reactors. The catalyst as a slurry oras a dry free flowing powder can be injected regularly to the reactorloop, which can itself be filled with circulating slurry of growingpolymer particles in a diluent. Hydrogen, optionally, may be added as amolecular weight control. The reactor may be maintained at a pressure offrom 27 bar to 45 bar, or preferably from 36 bar to 43 bar and at atemperature in the range of from 38° C. to 121° C., or preferably from60° C. to 105° C. Reaction heat can be removed through the loop wallsince much of the reactor is in the form of a double-jacketed pipe. Theslurry may exit the reactor at regular intervals or continuously to aheated low pressure flash vessel, rotary dryer and a nitrogen purgecolumn in sequence for removal of the diluent and all unreacted monomerand comonomers. The resulted hydrocarbon free powder can then becompounded for use in various applications. Alternatively, other typesof slurry polymerization processes can be used.

[0026] In any of the types of polymerization processes described above,a catalyst is used to promote polymerization. Any catalyst capable ofpolymerizing polyolefins in a polymerization reactor is contemplated.For example, high activity metallocene catalyst systems, e.g., catalystsystems having an efficiency of 500 gPP/(gcat*hr) or more, may beutilized. Preferably, the catalyst has an efficiency of 2500gPP/(gcat*hr) or more. Even more preferably, the catalyst has anefficiency of 3500 gPP/(gcat*hr) or more, and alternatively, anefficiency of greater than 5000 gPP/(gcat*hr). Useful catalysts aredescribed in detail in U.S. Pat. No. 6,368,999, which catalystdescriptions are hereby incorporated by reference. In processesdescribed herein, the amount of active metallocene is preferably 1.5 wt% or less and the amount of metal alkyl scavenger is 12 wt % or less ofthe metallocene catalyst. A catalyst having a low amount of activemetallocene in combination with a low amount of metal alkyl scavenger,or no metal alkyl scavenger, has been discovered to have a highsensitivity to poisons, resulting in lower catalyst efficiencies, andtherefore lower polyolefin product yield. Certain aspects describedherein include providing increased catalyst efficiency.

[0027] Certain polymerization processes may employ Ziegler-Naltacatalysts for a period of time, which may be followed by the use ofmetallocene catalysts for additional polymerizations. For example, theprocess may include contacting propylene monomers with a Ziegler-Nattacatalyst system to form polyolefins. Contacting the propylene monomerswith a Ziegler-Natta catalyst system may generate poisons in the productmixture. At least a portion of the product mixture may be recycled andcombined with the propylene monomers to contact the Ziegler-Nattacatalyst system. The process may further include stopping theintroduction of Ziegler-Natta catalyst to the polymerization reactor tocease the polymerization. A metallocene catalyst system may then bepassed to the polymerization reactor to polymerize the propylenemonomers. In doing so, the metallocene catalyst efficiency may bereduced due to the poisons generated by the Ziegler-Natta polymerizationprocess. For example, the activity of metallocene catalysts exposed tothose poisons may be 50 gPP/(gcat*hr) or less. Although the specificpoisons and poison levels can vary widely, the term “poisons”, as usedherein, refers to substances which reduce the catalyst efficiency, andspecifically includes alcohols (e.g., methanol, isopropanol and ethanol)and halogen moeties (e.g., fluorides and organohalides such as methylchloride).

[0028] In one or more embodiments, a polymerization process is providedthat includes providing a catalyst slurry to a polymerization reactor,the catalyst slurry including a metallocene catalyst and a first oil.Suitable metallocene catalysts are represented by the formula:

[0029] wherein: M is a metal of Group 4, 5, or 6 of the Periodic Tablepreferably, zirconium, hafnium and titanium, most preferably zirconium;

[0030] R¹ and R² are identical or different, preferably identical, andare one of a hydrogen atom, a C₁-C₁₀ alkyl group, preferably a C₁-C₃alkyl group, a C₁-C₁₀ alkoxy group, preferably a C₁-C₃ alkoxy group, aC₆-C₁₀ aryl group, preferably a C₆-C₈ aryl group, a C₆-C₁₀ aryloxygroup, preferably a C₆-C₈ aryloxy group, a C₂-C₁₀ alkenyl group,preferably a C₂-C₄ alkenyl group, a C₇-C₄₀ arylalkyl group, preferably aC₇-C₁₀ arylalkyl group, a C₇-C₄₀ alkylaryl group, preferably a C₇-C₁₂alkylaryl group, a C₈-C₄₀ arylalkenyl group, preferably a C₈-C₁₂arylalkenyl group, or a halogen atom, preferably chlorine; or aconjugated diene which is optionally substituted with one or morehydrocarbyl, tri(hydrocarbyl)silyl groups or hydrocarbyl,tri(hydrocarbyl)silylhydrocarbyl groups, said diene having up to 30atoms not counting hydrogen;

[0031] R⁵ and R⁶ are identical or different, preferably identical, areone of a hydrogen atom, a halogen atom, preferably a fluorine, chlorineor bromine atom, a C₁-C₁₀ alkyl group, preferably a C₁-C₄ alkyl group,which may be halogenated, a C₆-C₁₀ aryl group, which may be halogenated,preferably a C₆-C₈ aryl group, a C₂-C₁₀ alkenyl group, preferably aC₂-C₄ alkenyl group, a C₇-C₄₀ arylalkyl group, preferably a C₇-C₁₀arylalkyl group, a C₇-C₄₀ alkylaryl group, preferably a C₇-C₁₂ alkylarylgroup, a C₈-C₄₀ arylalkenyl group, preferably a C₈-C₁₂ arylalkenylgroup, a —NR₂ ¹⁵, —SR¹⁵, —OR¹⁵, —OSiR₃ ¹⁵ or —PR₂ ¹⁵ radical, wherein:R¹⁵ is one of a halogen atom, preferably a chlorine atom, a C₁-C₁₀ alkylgroup, preferably a C₁-C₃ alkyl group, or a C₆-C₁₀ aryl group,preferably a C₆-C₉ aryl group;

[0032] R⁷ is

[0033] —B(R¹⁴)—, ^(—)Al(R¹⁴)—, —Ge—, —Sn—, —O—, —S—, —SO—, —SO₂—,—N(R¹⁴)—, —CO—, —P(R¹⁴)—, or —P(O)(R¹⁴)—;

[0034] wherein: R¹⁴, R¹⁵and R¹⁶ are identical or different and are ahydrogen atom, a halogen atom, a C₁-C₂₀ branched or linear alkyl group,a C₁-C₂₀ fluoroalkyl or silaalkyl group, a C₆-C₃₀ aryl group, a C₆-C₃₀fluoroaryl group, a C₁-C₂₀ alkoxy group, a C₂-C₂₀ alkenyl group, aC₇-C₄₀ arylalkyl group, a C₈-C₄₀ arylalkenyl group, a C₇-C₄₀ alkylarylgroup, or R¹⁴ and R¹⁵, together with the atoms binding them, form acyclic ring; preferably, R¹⁴, R¹⁵and R¹⁶ are identical and are ahydrogen atom, a halogen atom, a C₁-C₄ alkyl group, a CF₃ group, a C₆-C₈aryl group, a C₆-C₁₀ fluoroaryl group, more preferably apentafluorophenyl group, a C₁-C₄ alkoxy group, in particular a methoxygroup, a C₂-C₄ alkenyl group, a C₇-C₁₀ arylalkyl group, a C₈-C₁₂arylalkenyl group, or a C₇-C₁₄ alkylaryl group;

[0035] or, R⁷ is represented by the formula:

[0036] wherein: R¹⁷ to R²⁴ are as defined for R¹ and R², or two or moreadjacent radicals R¹⁷ to R²⁴, including R²⁰ and R²¹, together with theatoms connecting them form one or more rings; preferably, R¹⁷ to R²⁴ arehydrogen;

[0037] M² is carbon, silicon, germanium or tin;

[0038] the radicals R³, R⁴, and R¹⁰ are identical or different and havethe meanings stated for R⁵ and R⁶, or two adjacent R¹⁰ radicals arejoined together to form a ring, preferably a ring containing from about4-6 carbon atoms.

[0039] Preferably, the metallocene catalyst is one of the highefficiency metallocene catalysts described above. The catalyst slurrypreferably includes 75 wt % or more of the first oil and 25 wt % or lessof the metallocene catalyst. More preferably, the catalyst slurryincludes from 90 wt % to 60 wt % first oil and from 10 wt % to 40 wt %metallocene catalyst. The first oil may be or include a mineral oilhaving a kinematic viscosity of from 0.63 centistokes (cSt) to 200 cStat 40° C. Preferably, the mineral oil has a kinematic viscosity of from50 cSt to 100 cSt, or from 45 cSt to 65 cSt, or from 25 cSt to 85 cSt.Preferably the first oil is or includes paraffinic mineral oil, such asKaydol white oil commercially available from Witco Corporation The firstoil may include mineral oil in amount greater than 95 wt %. Morepreferably the first oil includes 100 wt % mineral oil, i.e., the firstoil is “pure” mineral oil. A schematic diagram that illustrates anexample of the process is shown in FIG. 1.

[0040] The polymerization process preferably further includes providinga transport medium that includes a second oil. It has been discoveredthat providing the transport medium reduces catalyst particle attritionin process pumps. The second oil preferably has the same composition asthe first oil, i.e., mineral oil. More preferably, the second oil has aviscosity that is lower than the viscosity of the catalyst slurry. Forexample, the second oil preferably has a kinematic viscosity of from0.63 cSt to 200 cSt at 40° C. One purpose of the transport medium is toprotect catalyst efficiency, e.g., to maintain the catalyst efficiencyin comparison to catalyst systems not encountering poisons. The barrierproperties of the transport medium preferably reduce the high activitycatalyst system's sensitivity to poisons produced in the polymerizationprocess.

[0041]FIG. 1 illustrates a system that may be employed for providing acatalyst slurry to a polymerization reactor 100. In order to maintain ahomogeneous catalyst slurry, the catalyst slurry may be introduced to afirst vessel 102 to maintain the metallocene catalyst suspended in thefirst oil. The first vessel 102 includes a mixer (not shown) configuredto maintain uniform suspension of the metallocene catalyst particles inthe first oil. Preferably, upon transfer from the first vessel 102 toanother vessel or reactor, the catalyst slurry maintains the same solidsconcentration as upon introduction to the first vessel 102. For example,the first vessel 102 may include an anchor type mixer, e.g., a membershaped in the form of an anchor having a base proximate the base of thefirst vessel 102.

[0042] The first vessel 102 may include a catalyst slurry inlet 104, acatalyst slurry outlet 106 and a housing 108 having an upper portion anda lower portion. The lower portion may be disposed proximate thecatalyst slurry outlet 106 and have a proximal end nearest the catalystslurry inlet 104 and a distal end nearest the catalyst slurry outlet106. The process may include passing a different catalyst to thepolymerization reactor 100 at different times. Therefore, the firstvessel 102 should be designed for complete displacement of the catalystsolids, e.g., flushing. The lower portion of the first vessel 102 shouldhave a surface that is angled to encourage the catalyst to collect in aparticular area. As used herein, “angled” is a plane greater than 0° andless than 90° from horizontal. In at least one embodiment, the surfaceis substantially conical. One way to flush the first vessel 102 is bypassing a fluid, such as the first oil, through the first vessel 102, toremove any remaining catalyst slurry prior to filling the first vessel102 with a different catalyst slurry. Accordingly, the proximal endpreferably has a circumference that is greater than the circumference ofthe distal end, thereby facilitating cleaning of the first vessel 102between polymerizations. The first vessel 102 may be sized based onindividual system requirements. Mixing the catalyst slurry in the firstvessel 102 operates to minimize catalyst particle attrition and providefor a higher catalyst solids concentration than systems not employing acatalyst slurry including a first oil.

[0043] The first vessel 102 may also have a first oil inlet 110 toreceive additional amounts of the first oil to flush the first vessel102. The first vessel 102 may be flushed in between polymerization runs.Alternatively, the first vessel 102 may be flushed prior to changing thecatalyst to be disposed in the first vessel 102. As a result of theangled surface, e.g., the substantially conical portion, flushing thefirst vessel 102 results in improved removal of the catalyst slurry fromthe first vessel 102 in comparison to vessels not having a conicalportion.

[0044] The process may further include passing the catalyst slurry froma first vessel 102 to a second vessel 112 prior to introducing thecatalyst slurry into the polymerization vessel 100. The second vessel112 may have a catalyst slurry inlet 114 and a catalyst slurry outlet116 respectively configured to receive and discharge the catalystslurry. Furthermore, the second vessel 112 may have a angled lowersurface, e.g., a substantially conical portion, and a volume that issmaller than the volume of the first vessel 102. The second vessel 112may be used to meter, e.g., measure, the catalyst addition rate into thepolymerization vessel 100. As a result, the second vessel 112 volumeneed only be large enough to adequately meter the catalyst slurry andprovide a sufficient volume of catalyst slurry to the polymerizationvessel 100. Alternatively, metering may occur in the first vessel 102.The metering may include passing the catalyst slurry through at leastone flow monitoring device (not shown) configured to measure a catalystaddition rate. Alternatively, the catalyst addition rate may bemonitored via gear pumps (not shown) disposed in the conduit operablyconnected to the catalyst slurry outlet 116. The catalyst slurry exitingthe second vessel 112 generally has a low pressure. Therefore, thepressure of the catalyst mixture may be increased by passing thecatalyst mixture through one or more gear pumps. A second oil may beintroduced into the one or more gear pumps to prevent catalyst particledamage from the gear pumps. A preferred “flow monitoring device” can bewhat is commonly recognized or referred to in the polymerization reactorindustry as a “meter” including a member configured to measure the rateof the catalyst slurry flowing therethrough.

[0045] The transport medium 118 and the catalyst slurry are combined inthe one or more gear pumps to form a catalyst mixture 120, which issubsequently introduced to the polymerization vessel 100. Preferably,the catalyst mixture 120 includes from 25 wt % to 75 wt % catalystslurry and from 25 wt % to 75 wt % transport medium. The catalystmixture 120 is then introduced to the polymerization reactor 100 so thatthe propylene monomers are contacted with the catalyst mixture 120 topolymerize the propylene monomers and form polypropylene. Polymerizationoccurs in polymerization vessel 100 as described above.

Feed Stream Purification

[0046] In one or more embodiments, a polymerization process is providedthat includes contacting olefin monomers with a supported metallocenecatalyst to polymerize the monomers and form a product mixture thatincludes macromers and/or polymers, unreacted or partially reactedmonomers, and poisons. Preferably, the olefin monomers have from two tosixteen carbon atoms. More preferably, the olefin monomers includepropylene, ethylene, or combinations thereof. The product mixture mayinclude poisons in an amount of 2.5 ppm or more. Preferably, thesupported metallocene catalyst system is a high efficiency metallocenecatalyst system as described above.

[0047] The polymerization process may occur in a system utilizing aspecific catalyst system for a polymerization run, such as aZiegler-Natta catalyst system, and subsequently using a differentcatalyst system for another polymerization run, such as a metallocenecatalyst system. For example, the process may include contactingpropylene monomers with a Ziegler-Natta catalyst system to formpolypropylene, thereby generating poisons in the product mixture. Atleast a portion of the product mixture may be recycled and combined withmonomers to contact the Ziegler-Natta catalyst system. The process mayfurther include stopping the flow of Ziegler-Natta catalyst to thepolymerization reactor to cease the polymerization based on thatparticular catalyst system. A metallocene catalyst system may then beintroduced to the polymerization reactor to polymerize the monomers.However, “poisons”, such as organohalides and alcohols produced by theZiegler-Natta catalysts are still present and may reduce the efficiencyof the metallocene catalyst system. The product mixture includingpoisons may then be combined with the “fresh” propylene monomers to passthrough the polymerization reactor and contact the metallocene catalystsystem. The fresh propylene feed stream may include a small amount ofimpurities, which may also function as poisons. High efficiency, andtherefore high yield, polymerization catalysts are particularlysensitive to poisons as a result of a low amount of metal alkylscavenger present in the catalyst. Therefore, the poison level should bereduced prior to passing monomers through a polymerization process.Additionally, the process may further include removing a portion of theproduct mixture and passing it through a removal device includingzeolite particles supported by a mesh screen, the zeolite particleshaving a pore size of from 6 Å to 16 Å, thereby preventing the passageof molecules having a size of greater than 16 Å therethrough. In doingso, at least a portion of poisons from the product mixture aretransferred to the zeolite particles providing a purified monomer streamhaving poisons in an amount of 1 ppm or less. More preferably, thepurified monomer stream has poisons in an amount of 0.5 ppm or less.

[0048] Preferably, the removal device (discussed in further detailbelow) includes molecular sieve particles having an average pore size offrom 6 Å to 16 Å. As used herein, the term “molecular sieve” means astructure having a high surface area to prevent the passage of specifiedmolecules therethrough, such as molecules having a critical diameter ofup to 10 Å. For example, the molecular sieve unit may include an X typemolecular sieve. A type X structured zeolite is characterized by FormulaI below:

[0049] Formula I: (0.9+−0.2)M₂/nO:Al₂O₃(2.5+−0.5)SiO₂:yH₂O; where Mrepresents at least one cation having a valence of not more than 3, nrepresents the valence of M and y is a value up to 8 depending upon theidentity of M and the degree of hydration of the crystal. The cation Mmay be one or more of a number of cations such as a hydrogen cation, analkali metal cation, or an alkaline earth cation or other selectedcations and is generally referred to as an exchangeable site. The type Xzeolite can be present in the base material in concentrations generallyranging from 75 wt % to 90 wt % of the base material based on a volatilefree composition. The remaining material in the base material preferablycomprises amorphous silica or alumina or both, which are present inintimate mixture with the zeolite material.

[0050] More preferably, the molecular sieve unit includes a 13×molecular sieve commercially available from UOP of Des Plaines, Ill..The UOP 13× molecular sieve has an average pore size of 10 Å, whichallows it to adsorb molecules having a critical diameter of smaller than10 Å.

[0051] Contacting an input stream with the removal device describedherein preferably results in a purified output stream having poisons inan amount of 1 ppm or less. In certain embodiments, the input stream haspoisons in an amount of 2.5 ppm or more, and in certain otherembodiments, the input stream has poisons in an amount of 5 ppm or more,e.g., up to 10 ppm or more poisons content. As a result of the low levelof poisons present in the output stream, the metallocene catalyst hasexperienced an efficiency of greater than 3500 gPP/(gcat*hr), andalternatively, an efficiency of greater than 5000 gPP/(gcat*hr). Incertain embodiments, the input stream is the recycle stream, prior tocombining with the fresh feed stream, in which case the output stream isadded to the fresh feed stream. Preferably, however the input stream isa combination of the recycle stream and the fresh feed stream.

[0052]FIG. 2 illustrates a cross-sectional view of an embodiment of aremoval device 200, useful with embodiments of the present. invention.The removal device 200 includes a shell 202 in which at least one firstsupport member 204 is positioned. The first support member 204 includesa number of perforations (e.g., holes) to allow a monomer stream flowthrough the first support member 204. The first support member 204 ispreferably positioned between the feed inlet 203 and the feed outlet 205of the removal device 200 and contacts a first portion of molecularsieve particles 206 which are positioned on a side of the first supportmember 204 closest to the feed outlet 205. The first support member 204may include one or more screens 210 positioned thereon to furtherseparate and support the first portion of molecular sieve particles 206.Mesh screen 210 may have a particle size of 8×12 mesh or less. The firstportion of molecular sieve particles preferably has a size of 8×12 meshor greater. The shell 202 may further include a screen 210 positionedabove the first portion 206 to separate the first portion 206 from asecond portion 208 of molecular sieve particles. The screen 210 may havea particle size of 4×8 mesh or less and the second portion of molecularsieve particles preferably has a particle size of greater than or equalto 4×8 mesh. The molecular sieve particles 212 are preferably uncrushed.The removal device 200 may also include a screen 214 provided to limitthe amount of molecular sieve particles that flow out of the removaldevice 200 through the feed outlet 205.

[0053]FIG. 3 illustrates a polymerization process wherein the recyclestream is mixed with a “fresh” feed stream, e.g., a monomer stream thathas not been subjected to polymerization in the polymerization vessel100, to form an input stream prior to purification. The process includescontacting the input stream, e.g., a first monomer stream 300, with oneor more removal devices 302 to form a second monomer stream 304. Theprocess further includes contacting the second monomer stream 304 with ametallocene catalyst system in a polymerization vessel 306 to polymerizethe propylene to produce polyolefins in a third stream 308. Preferably,the first monomer stream 300 includes ethylene, propylene and higheralpha-olefin monomers having from four to sixteen carbon atoms. Morepreferably, the first monomer stream 300 includes propylene. Morespecifically, the first monomer stream 300 preferably includes freshpropylene. The first monomer stream 300 preferably is flowing to removaldevice 302 at a flowrate of from 3700 kg/hr to 56000 kg/hr. In additionto including fresh propylene, the first monomer stream 300 may includepoisons, which reduce the efficiency of the metallocene catalyst system.It is preferred that these contaminants be less than 1 ppm of themixture entering the polymerization vessel 306, e.g., the “inputstream.” Therefore, the first monomer stream 300 passes through theremoval device 302 to remove at least a portion of the poisons from thepropylene prior to subsequent polymerization.

[0054] As a result of passing through the one or more removal devices302, the second monomer stream 304 has a reduced concentration ofpoisons in comparison to the first monomer stream 300. Preferably, thesecond monomer stream 304 has 1 ppm or less poisons. More preferably,the second monomer stream 304 includes less than 0.5 ppm poisons.

[0055] The polymerization process further includes contacting the secondmonomer stream 304 with a metallocene catalyst system to producepolyolefins in a third stream 308. Preferably, the second monomer stream304 is entering the reactor 306 at a flow rate of from 3700 kg/hr to56000 kg/hr. The third stream 308 preferably exits the reactor 306 at aflowrate of from 3700 kg/hr to 56000 kg/hr.

[0056] The polymerization process may further include separatingun-polymerized monomers from the third stream 308 to form a fourthmonomer stream 310, e.g., a recycle stream, and a polyolefin stream 312.The polyolefin stream 312 may be separated from the fourth monomerstream 310 via a separator 314, or by any other process known in the artfor separating unreacted olefin monomers from formed polyolefins. Thefourth monomer stream 310 includes unpolymerized monomers plus otherinert liquids and gases. In addition, the fourth monomer stream 310includes poisons, which may be present in an amount of 5 ppm or more.The fourth monomer stream 310 preferably has a flowrate of from 7 klb/hrto 105 klb/hr. The fourth monomer stream 310 may be subsequentlycombined with the first monomer stream 300 to form a mixed monomerstream 316. The first monomer stream 300 and the fourth monomer stream310 may be combined in an amount determined by individual systemrequirements. Preferably, the first monomer stream 300 and the fourthmonomer stream 310 are combined in equal amounts. When combined in equalamounts, the mixed monomer stream 316 may include poisons in an amountof 2.5 ppm or more. In the alternative, the fourth monomer stream 310may directly contact the one or more molecular sieve units 302.

[0057] Catalyst Delivery

[0058] Certain embodiments include providing a conduit 400 that isoperably connected to a polymerization vessel 404 to deliver catalyst tothe polymerization vessel 404, as shown in FIG. 4. A catalyst can beintroduced to the conduit 400 through a catalyst inlet 402. The catalystinlet 402 may be a conduit having an inlet 418 and an outlet 420, theoutlet being disposed within the conduit 400. The catalyst is generallysuspended in a liquid phase. Alternatively, the catalyst may be in theform of free-flowing powder. The free-flowing powder may beconducted/transferred through the conduit 400 by an inert gas. The term“conduit” as used herein refers to any piping, etc. configured to pass acatalyst therethrough. Desirably, the conduit 400 is a pipe having adiameter of from 0.0120 m to 0.00635 m. The catalyst may include ametallocene system or a Ziegler-Natta system, or any other catalystcapable of polymerizing olefins. When using a metallocene catalyst, themethod may include combining a carrier, such as an inert fluid, with themetallocene catalyst prior to introducing the metallocene catalyst tothe polymerization vessel 404 to transport the metallocene catalystthrough the conduit 400. The inert fluid may be an oil having akinematic viscosity of from 0.63 cSt to 200 cSt at 40° C. When utilizinga Ziegler-Natta catalyst system, the method may include combining aliquid solvent, such as hexane, with the Ziegler-Natta catalyst prior tointroducing the Ziegler-Natta catalyst to the polymerization vessel 404.

[0059] In addition, the conduit 400 preferably has a first monomerstream inlet 406. A first monomer stream 409 including propylenemonomers can be introduced to the conduit 400 through the first monomerstream inlet 406 to provide a mixed catalyst stream (a mixture ofcatalyst and monomers) upon monomer contact with the catalyst, e.g.,when the catalyst is injected into the first monomer stream 418. Themonomer is preferably the same monomer as the monomer being polymerizedin the polymerization vessel 404. For example, the monomer is preferablypropylene. The mixed catalyst stream operates to increase the velocityof the catalyst entering the polymerization vessel 404. The firstmonomer stream inlet 406 may include a first conduit 407 having a firstmonomer valve 408. The first monomer valve 408 operates to provide amixed catalyst stream having a velocity sufficient to prevent pluggingof the conduit 400 during polymerization processes. The mixed catalyststream velocity is dependent on individual system requirements, such asthe conduit diameter.

[0060] During a typical polymerization operation, the conduit 400 mayexperience plugging, e.g., a stoppage of the catalyst flow through theconduit 400, in at least one portion of the conduit 400. Plugging mayresult from polymerization within the conduit 400 upon catalyst contactwith the monomer used to transfer the catalyst into the reactor 404. Asa result, at least a portion of the conduit 400 may need to be servicedto remove the plug. Complete replacement of the conduit 400 may requirethe polymerization process to cease while the conduit 400 is replaced.It is desirable that the polymerization continues while the conduit 400is serviced, e.g., the flow of the catalyst passing through the conduit400 may be terminated while maintaining the polymerization. Althoughpolymerization vessels may include an alternate catalyst injectionsystem 422, many vessels do not have the ability to prevent flow of thepolymer into the conduit being serviced. Therefore, the conduit 400 mayinclude a first portion 424 that may be removed upon at least partialplugging, or at any other time when the system requires maintenance. Todetermine when the conduit 400 needs to be replaced, e.g., uponplugging, the process may include monitoring the conduit 400 to identifyplugging. Closing a first catalyst valve 410 and the first monomer valve408 may stop the flow. Upon stopping the flow of the catalyst throughthe conduit 400, a second monomer stream 419 may be introduced to theconduit 426 through a second monomer stream inlet 412, which is locateddownstream of the first monomer stream inlet 406 and passed to thepolymerization vessel 404. The second monomer stream 419 flows to thepolymerization vessel 404 during the repair/replacement of the pluggedconduit portion. The second monomer inlet 412 may include a secondconduit 413 having a second monomer valve 414. Alternatively, the secondmonomer stream 419 may flow through a second conduit 426 to thepolymerization vessel 404, rather than flowing through a portion of theplugged conduit 400. The second monomer stream 419 may flow to theconduit 426 at a velocity substantially equal to the velocity of thefirst monomer stream 409. For example, the second monomer stream 419 mayhave a velocity that is from 50% to 150% of the first monomer streamvelocity. Preferably, the second monomer stream 419 has a velocity thatis from 80% to 120% of the first monomer stream velocity.

[0061] The section of the conduit 400 that experiences plugging, or anyother section that should be removed/replaced is then removed (or theflow is diverted to a second conduit) and the removed section of theconduit 400 is replaced with a different conduit section. The conduit400 may include a first catalyst valve 410 and a second catalyst valve416, the first catalyst valve 410 being disposed in the first section424 to regulate the flow of catalyst and the second catalyst valve 416being disposed in a second section 426 between the first monomer streaminlet 406 and the second monomer stream inlet 412. The first valve 410and the second valve 416 may include more than one valve and the firstsection 424 and a flange 428 may connect the second section 426 to thefirst section 424. The flange 428 provides easy removal of eitherportion for conduit maintenance. The second catalyst valve 416 isconfigured to hold a backpressure to prevent the flow of polymerizablepropylene monomers into the conduit 400 from the polymerization vessel404. Preferably, the second catalyst valve 416 is a tight sealinghigh-pressure valve. The valve pressure depends on individual reactorpressures.

[0062] The removed section may be the section of the conduit 400 betweenthe first catalyst valve 410 and the second catalyst valve 416.Alternatively, the removed section may be the first section 424, e.g.,the conduit section including the catalyst inlet 418 up to the flange428. The conduit 400 preferably includes multiple sections, such as asection between the first catalyst valve 410 and the second catalystvalve 416, to accommodate removal of only a portion of the conduit 400.The multiple sections may be connected by methods known in the art forconnecting the multiple sections, for example threads or flanges. Theremoved section may be rehabilitated for re-use. During maintenance,additional catalyst may flow to the reactor 404 via a second conduit422. The second conduit 422 is essentially similar to the conduit 400.In the absence of an operable second conduit 422, the removable conduit400 provides minimal production stoppage as a result of the continuousmonomer flow to the reactor 404. Once the fouled section of conduit 400is replaced, the catalyst flow is returned to the conduit 400 and theflow of the second monomer stream 419 can be terminated.

[0063] The foregoing methods, either alone or in combination, result ina deceased effect of poisons on metallocene catalyst systems. As aresult, the metallocene catalyst systems experience increasedefficiency.

[0064] Having now fully described this invention, it will be appreciatedby those skilled in the art that the invention can be performed within awide range of parameters within what is claimed, without departing fromthe spirit and scope of the invention. Where applicable all patents,applications, and publications cited herein, including those relied uponfor priority, are herein incorporated by reference.

What is claimed is:
 1. A method of producing a polyolefin, comprising:contacting a first stream with at least one removal device to form asecond stream, wherein the at least one removal device comprisesmolecular sieve particles having an average pore size of from 6 Å to 16Å; contacting the second stream with a catalyst system to produce thepolyolefins in a third stream including the polyolefin and unpolymerizedolefins; separating un-polymerized olefins from the third stream to forma fourth stream; combining the fourth stream with the first stream toform a mixed stream; and contacting the mixed stream with the at leastone removal device to form the second stream.
 2. The method of claim 1,wherein the polyolefin comprises polypropylene.
 3. The method of claim1, wherein the catalyst system comprises a metallocene catalyst system.4. The method of claim 1, wherein the second stream comprises less than1 ppm of alcohols, halogen moeties, and organohalides.
 5. The method ofclaim 1, wherein the first stream comprises fresh propylene.
 6. Themethod of claim 1, wherein the first stream comprises alpha-olefinmonomers selected from the group selected of ethylene, propylene, andalpha-olefins having from four to 16 carbon atoms.
 7. The method ofclaim 1, wherein the at least one removal device comprises a shellhaving a first support member.
 8. The method of claim 1, wherein the atleast one removal device comprises a shell having a first support memberin contact with at least a first portion of one or more molecular sieveparticles.
 9. The method of claim 1, wherein the at least one removaldevice comprises a shell having a first support member disposed adistance from at least a second portion of the one or more molecularsieve particles.
 10. The method of claim 1, wherein the first stream hasa flow rate of from 3700 kg/hr to 56000 kg/hr.
 11. The method of claim1, wherein the second stream has a flow rate of from 3700 kg/hr to 56000kg/hr.
 12. The method of claim 1, wherein the third stream has a flowrate of from 3700 kg/hr to 56000 kg/hr.
 13. The method of claim 1,wherein the fourth stream has a flow rate of from 2600 kg/hr to 56000kg/hr.
 14. The method of claim 1, in which the metallocene catalyst hasan efficiency greater than 3500 gPP/(gCat*hr).
 15. The method of claim1, in which the one or more molecular sieve particles comprise a 13×molecular sieve.
 16. The method of claim 1, wherein the second streamcomprises less than 0.5 ppm of alcohols, halogen moeties andorganohalides.
 17. The method of claim 1, wherein the fourth streamcomprises 5 ppm or more alcohols, halogen moeties and organohalides. 18.The method of claim 1, wherein the one or more molecular sieve particleshave a size of 8 by 14 mesh.
 19. The method of claim 1, wherein themetallocene catalyst has an efficiency greater than 3500 gPP/(gCat*hr).20. The method of claim 1, wherein the metallocene catalyst comprises1.5 wt % or less active metallocene and 12 wt % or less of metal alkylscavenger.
 21. A method of producing polypropylene, comprising:contacting a first monomer stream comprising propylene monomers with asupported metallocene catalyst to form a product comprisingpolypropylene, unpolymerized propylene monomers, organohalides andalcohols; providing a second monomer stream comprising at least aportion of the product; passing at least a portion of the second monomerstream through a removal device comprising molecular sieve particlessupported by a mesh screen having a pore size of from 6 Å to 16 Å toform a third stream, wherein at least a portion of the alcohols andorganohalides from the second monomer stream are absent from the thirdstream; and contacting at least a portion of the third stream with asupported metallocene catalyst to form additional polypropylene.
 22. Amethod of producing polypropylene, comprising: passing a propylene feedstream through one or more removal devices to form a purified monomerstream, wherein the propylene feed stream has alcohols and organohalidesin an amount greater than 5 ppm and the purified monomer streamcomprises alcohols and organohalides in an amount less than 1 ppm;contacting the purified monomer stream with a supported metallocenecatalyst to polymerize the purified monomer stream and form a productmixture that includes polypropylene macromers or polymers, unreacted orpartially reacted propylene monomers, alcohols and organohalides. 23.The method of claim 22, wherein the passing the propylene feed streamthrough one or more removal devices to form a purified monomer streamcomprises combining a first monomer stream and a second monomer stream,the first monomer stream comprising propylene monomers and the secondmonomer stream comprising unreacted or partially reacted propylenemonomers, alcohols and organohalides.
 24. The method of claim 22,wherein the passing the propylene feed stream through one or moreremoval devices to form a purified monomer stream comprises combining afirst monomer stream and a second monomer stream, the first monomerstream comprising propylene monomers and the second monomer streamcomprising unreacted or partially reacted propylene monomers, andalcohols and organohalides in an amount greater than 10 ppm.
 25. Themethod of claim 22, further comprising removing the polypropylenemacromers from the product mixture to form a recycle stream andcombining the recycle stream with the propylene feed stream.
 26. Amethod of producing polypropylene, comprising: contacting propylenemonomers with a supported metallocene catalyst to polymerize thepropylene monomers and form a product mixture that includespolypropylene macromers or polymers, unreacted or partially reactedpropylene monomers, alcohols and organohalides; removing a portion ofthe product mixture to form a recycle stream and passing it through aremoval device comprising zeolite particles having a pore size of from 6to 16 Å; transferring at least a portion of the alcohols andorganohalides from the recycle stream to the removal device to provide apurified recycle stream having alcohols and organohalides in an amountof 1 ppm or less; and contacting at least a portion of the purifiedrecycle stream with the supported metallocene catalyst to formpolypropylene.
 27. A removal device, comprising: a shell having a firstsupport member; and at least a first portion of one or more molecularsieve particles in contact with the first support member.
 28. Theremoval device of claim 27, wherein the molecular sieve particlescomprises 13× particles.
 29. The removal device of claim 27, wherein themolecular sieve particles are configured to remove at least a portion ofalcohols, halogen moeties and organohalides present in an olefin monomerstream passing therethrough.
 30. The removal device of claim 27, whereinthe molecular sieve particles are configured to reduce a level ofalcohols, halogen moeties and organohalides present in an olefin monomerstream passing therethrough from greater than 5 ppm or more to less than1 ppm.